Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 191754
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1254 PM CDT MON SEP 19 2016

.UPDATE...
Issued at 1031 AM CDT Mon Sep 19 2016

Fog burned off quickly this morning and skies are clear across the
area. Still expect today to be sunny except for some clouds moving
into the northern CWA ahead of a weak shortwave late this
afternoon. Still expect this afternoon to be dry, with the chance
of showers and thunderstorms waiting until this evening across
northeast Missouri and west central Illinois when the trough
passes through the area. Highs today will be in the upper 80s in
most areas as morning soundings showed the potential for mixing up
to 850mb.

Britt

&&

.SHORT TERM...  (Through Late This Afternoon)
Issued at 306 AM CDT Mon Sep 19 2016

Through sunrise...have issued a Dense Fog Advisory for the srn half
or so of the CWA. The areas most impacted will be low lying areas
and near water sources. However, counties across the ern portions of
the adv shud continue to see lower visbys as temps drop and moisture
pools along the sfc ridge axis. Further west, can not rule out fog
along rivers, but overall, should not be an issue.

Otherwise, not much change to the prev forecast for today. Fog
should burn off quickly with an otherwise clear sky. The sfc ridge
will continue to build ewd with winds becoming swly thru low levels
allowing a quick warm-up. Have continued to trend temps aoa the
warmer guidance.

The warm temps with somewhat good moisture return across wrn and nrn
portions of the CWA will allow CAPE values to jump above 2000 J/kg
by this afternoon. However, expect a strong cap to remain in place
and will delay convection across the area until at least this
evening.

Tilly

.LONG TERM...  (Tonight through Sunday)
Issued at 306 AM CDT Mon Sep 19 2016

Surface ridge moves off to the southeast by tonight with a weak cold
front approaching northern MO. Storms expected to develop along this
boundary, but just barely brush our northern counties as most of
energy and support will be to our north. Otherwise, clear to partly
cloudy skies expected with lows in the 60s.

By Tuesday, frontal boundary to weaken even more and wash out with
surface ridge building back in. So will will see dry and
unseasonably warm conditions for the rest of the work week. There is
a slight chance of activity to affect far northern portions of
forecast area, closer to surface boundary, Thursday and Thursday
night.

Then by the weekend will see increasing chances of storms as main
system approaches region. Extended models continue to slow down this
system, so backed off on pops for Saturday. Will see better chances
of storms for last half of weekend and into early next week. With
slower onset, will see warmer temps for Saturday, so raised them a
few degrees.

Byrd

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1254 PM CDT Mon Sep 19 2016

Dry and VFR conditions are expected through this evening. A front
will move into the area overnight which may produce isolated
showers and thunderstorms over west central Illinois. Do not have
enough confidence at this point to put this chance in the KUIN
TAF. Otherwise, expect there to be redevelopment of fog again late
tonight and early Tuesday, mainly along river valleys. Have placed
IFR visibilities at KSUS and KCPS between 08-13Z. Fog should
diminish by mid morning on Tuesday. Winds should be mainly light
through the period.

SPECIFICS FOR KSTL: Expect mainly dry and VFR conditions through
the period with light winds.

Britt

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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